Radio base station, wireless terminal, radio communication system, transmission power controlling method, control circuit and program storage medium

ABSTRACT

The present invention includes: a plurality of antenna sections, each of which to generate base station reception beams and to receive, by using the base station reception beams, one or more signals transmitted from a wireless terminal using one or more terminal transmission beams; a measurement unit that measures reception quality of each of the signals for each of the base station reception beams; and a control unit that groups the base station reception beams into groups in units of the antenna sections, and perform transmission power control on the terminal transmission beams of the wireless terminal in units of the groups, on the basis of a result of measurement of the measurement unit in units of the groups.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of copending application Ser. No.16/944,719, filed on Jul. 31, 2020, which is a Continuation ofInternational Application No. PCT/JP2018/004435, filed on Feb. 8, 2018,all of which are hereby expressly incorporated by reference into thepresent application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a radio base station, a wirelessterminal, a radio communication system, and a transmission powercontrolling method for controlling transmission power of the wirelessterminal.

2. Description of the Related Art

A wireless terminal that communicates with a radio base stationtypically controls transmission power of a signal transmitted therefromto the radio base station. This is to allow a signal transmitted by thewireless terminal to be received by the radio base station without anyerror, and to prevent unnecessary interference with other radio basestations.

The New Radio (NR) standard defined in the 3rd Generation PartnershipProject (3GPP) specifies two control methods, which are open-loop powercontrol and closed-loop power control, as transmission power controlmethods for wireless terminals, for application to the 5th GenerationMobile Communications Systems (Non Patent Literature 1).

The open-loop power control is a control method performed when awireless terminal starts communicating with a radio base station, orwhen a wireless terminal connects with another radio base station byhandover and starts communicating with the radio base station. In theopen-loop power control, the radio base station notifies the wirelessterminal of, a target reception power value of a preamble to betransmitted by the wireless terminal using a physical random accesschannel (PRACH) when starting communication as notification information.The wireless terminal calculates a path loss of downlink transmission(in the direction from the radio base station to the wireless terminal)from a reception power value of a signal transmitted periodically fromthe radio base station and a transmission power value of the radio basestation of which the wireless terminal is separately notified by theradio base station. Then, the wireless terminal determines transmissionpower of an uplink signal by adding a power value corresponding to thecalculated path loss to the target reception power value of thepreamble, of which the wireless terminal is notified by the radio basestation.

In contrast, the closed-loop power control is a control method forcontrolling transmission power of a wireless terminal by transmitting atransmission power control (TPC) command explicitly identifying anincrease or decrease in the transmission power by a radio base stationto the wireless terminal after communication is started. Whilecommunicating with the radio base station, the wireless terminal oncedetermines the transmission power value by the open-loop power control,adjusts the transmission power in accordance with the closed-loop powercontrol from the radio base station, and determines a final transmissionpower value (See, for example, Non Patent Literature 1: 3GPP TS 38.213V15.0.0 (2017-12)).

According to the NR standard, a configuration in which one radio basestation transmits signals from a plurality of antennas installed atdifferent locations, that is, a configuration in which one radio basestation includes a plurality of transmission reception points (TRPs) canbe considered. A TRP is a location at which the radio base stationactually transmits and receives signals, that is a location at which anantenna is installed. In a case where a wireless terminal transmitssignals by setting the same transmission power for all transmissionbeams, the reception powers of the signals from the wireless terminalmay be different among TRPs of a radio base station that includes aplurality of TRPs. In addition, interference powers from other wirelessterminals may also be different among the TRPs of the radio basestation. Moreover, the signal to interference plus noise power ratios(SINRs) of the signals from the wireless terminal may be different amongthe TRPs, and some TRPs may satisfy proper SINR values while other TRPsmay not.

With the technology described in Non Patent Literature 1, however,different transmission power control commands cannot be used for each ofthe TRPs. Thus, in a case where the SINRs of signals from a wirelessterminal are different among different TRPs and some TRPs satisfy properSINR values while the other TRPs do not, the transmission powers of thetransmission beams from the wireless terminal toward the TRPs can onlybe performed such that the transmission powers are increased ordecreased for all the TRPs according to the technology described in NonPatent Literature 1. There is thus a problem in that control for makingthe individual SINRs at the TRPs included in the radio base stationcloser to proper SINR values, cannot be performed.

The present invention has been made in view of the above, and an objectthereof is to provide a radio base station capable of controllingtransmission powers of signals transmitted by a wireless terminal inunits of locations at which the signals are received in a case wheresignals from a wireless terminal can be received at a plurality oflocations.

SUMMARY OF THE INVENTION

A radio base station according to the present invention includes: aplurality of base station antenna sections, each of which generates basestation reception beams, and receives, by using the base stationreception beams, one or more signals transmitted from a wirelessterminal using one or more terminal transmission beams. The radio basestation also includes a measurement unit that measures reception qualityof each of the signals for each of the base station reception beams. Theradio base station also includes a control unit that groups the basestation reception beams into groups in units of the base station antennasections, and performs transmission power control on the terminaltransmission beams of the wireless terminal in units of the groups onthe basis of a result of measurement of the measurement unit in units ofthe groups.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a configuration of aradio communication system according to a first embodiment.

FIG. 2 is a diagram illustrating an example of frequency mapping of asounding signal transmitted by a wireless terminal according to thefirst embodiment.

FIG. 3 is a table illustrating an example of selecting, for each basestation reception beam, a terminal transmission beam from the wirelessterminal achieving good reception quality at the radio base stationaccording to the first embodiment.

FIG. 4 is a diagram illustrating an example of a state in which theradio base station according to the first embodiment causes the wirelessterminal to transmit signals such as data by using specified terminaltransmission beams.

FIG. 5 is a diagram illustrating an example of a result of measurementof reception quality at each TRP of the radio base station according tothe first embodiment.

FIG. 6 is a diagram illustrating an example of a configuration of theradio base station according to the first embodiment.

FIG. 7 is a flowchart illustrating an operation of grouping terminaltransmission beams of the wireless terminal at the radio base stationaccording to the first embodiment.

FIG. 8 is a flowchart illustrating an operation when a wireless terminalto which a physical uplink shared channel (PUSCH) is to be assigned isselected in the radio base station according to the first embodiment.

FIG. 9 is a diagram illustrating an example of a configuration of thewireless terminal according to the first embodiment.

FIG. 10 is a flowchart illustrating an operation until the wirelessterminal according to the first embodiment acquires group information ofterminal transmission beams of the wireless terminal from the radio basestation.

FIG. 11 is a flowchart illustrating an operation of the wirelessterminal according to the first embodiment when a PUSCH is assigned tothe wireless terminal by the radio base station.

FIG. 12 is a diagram illustrating a hardware configuration forimplementing the radio base station and the wireless terminal accordingto the first embodiment.

FIG. 13 is a diagram illustrating an example of a configuration of aradio communication system according to a second embodiment.

FIG. 14 is a table illustrating an example of information on therelation of TRP group IDs and base station transmission beams of which aradio base station notifies a wireless terminal in the secondembodiment.

FIG. 15 is a table illustrating the association between base stationtransmission beams selected from a result of measurement of receptionquality for each of terminal reception beams and the terminal receptionbeams in the wireless terminal according to the second embodiment.

FIG. 16 is a diagram illustrating an example of a configuration of aradio base station according to the second embodiment.

FIG. 17 is a flowchart illustrating an operation of transmitting ameasurement signal and control information to a wireless terminal thatgroups terminal reception beams in the radio base station according tothe second embodiment.

FIG. 18 is a diagram illustrating an example of a configuration of thewireless terminal according to the second embodiment.

FIG. 19 is a flowchart illustrating an operation of grouping terminaltransmission beams of a wireless terminal in the wireless terminalaccording to the second embodiment.

FIG. 20 is a diagram illustrating an example of a mapping pattern inwhich a wireless terminal according to a fourth embodiment maps onecodeword in all the terminal transmission beams to be used fortransmission.

FIG. 21 is a diagram illustrating an example of a mapping pattern inwhich the wireless terminal according to the fourth embodiment maps onecodeword in units of terminal transmission beams.

FIG. 22 is a flowchart illustrating an operation of determining atransmission power controlling method for a wireless terminal in theradio base station according to the fourth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A radio base station, a wireless terminal, a radio communication system,and a transmission power controlling method according to certainembodiments of the present invention will be described in detail belowwith reference to the drawings. Note that the present invention is notlimited to the embodiments.

First Embodiment

In the present embodiment, assume a radio communication system, in whichthe wireless terminal generates a transmission beam and the radio basestation generates a reception beam to perform radio communicationtherebetween when a radio base station receives a signal transmittedfrom a wireless terminal. While a case where the radio base stationincludes two TRPs will be described in the present embodiment, thenumber of TRPs of the radio base station is not limited to two.Hereinafter, one or more beams associated with one TRP will be referredto as a TRP group. Specifically, a reception beam generated by one TRPin the radio base station belongs to one TRP group, and one or moretransmission beams generated to be directed toward one TRP by thewireless terminal also belongs to one TRP group. The radio base stationapplies a transmission power control command in units of TRP groups,that is, controls transmission power of transmission beams of thewireless terminal in units of TRP groups. In the description below, atransmission beam generated by the wireless terminal will be referred toas a terminal transmission beam, and a reception beam generated by theradio base station will be referred to as a base station reception beam.

First, a method for determining association between a plurality ofterminal transmission beams generated by the wireless terminal and a TRPwill be explained. FIG. 1 is a diagram illustrating an example of aconfiguration of a radio communication system 50 according to the firstembodiment of the present invention. The radio communication system 50includes a radio base station 10, and a wireless terminal 20. The radiobase station 10 includes a signal processing unit 17, and antennasections 14 a and 14 b. Hereinafter, the locations at which the antennasections 14 a and 14 b are installed will be referred to as TRP #1 andTRP #2, respectively. The radio base station 10 performs radiocommunication with the wireless terminal 20 by using the antennasections 14 a and 14 b. The antenna sections 14 a and 14 b each generatefour base station reception beams, and receive signals transmitted fromthe wireless terminal 20 by using the base station reception beams.

In the example of FIG. 1, the base station reception beams generated bythe antenna section 14 a will be referred to as base station receptionbeams 101 to 104, and the base station reception beams generated by theantenna section 14 b will be referred to as base station reception beams105 to 108. The wireless terminal 20 generates six terminal transmissionbeams 201 to 206, and transmits signals to the radio base station 10 byusing the terminal transmission beams 201 to 206. While the number ofwireless terminals 20 in the radio communication system 50 is one inFIG. 1, this is one example, and the number of wireless terminals 20 maybe two or more.

In the radio communication system 50 illustrated in FIG. 1, the wirelessterminal 20 first transmits sounding signals by using the terminaltransmission beams 201 to 206 that are all the beams which can begenerated. A sounding signal is a measurement signal used for measuringthe reception quality of a signal received by the radio base station 10.The sounding signals are used for associating a plurality of terminaltransmission beams with a TRP. The radio base station 10 receives thesounding signals by using the base station reception beams 101 to 108,and measures the reception quality of each sounding signal for each basestation reception beam. Note that, in a case where the wireless terminal20 cannot generate all of the terminal transmission beams 201 to 206 atthe same time, the wireless terminal 20 may generate the terminaltransmission beams at different timings. In other words, the wirelessterminal 20 may generate the terminal transmission beams 201 to 206separately at multiple timings. In a similar manner, in a case where theradio base station 10 cannot generate all of the base station receptionbeams 101 to 108 at the same time, the radio base station 10 maygenerate the base station reception beams at different timings. In otherwords, the radio base station 10 may generate the base station receptionbeams 101 to 108 separately at multiple timings. In the presentembodiment, an example in which the wireless terminal 20 is capable ofgenerating all of the terminal transmission beams 201 to 206 at the sametime, and the radio base station 10 is capable of generating all of thebase station reception beams 101 to 108 at the same time will bedescribed.

The radio base station 10 selects a terminal transmission beam from thewireless terminal 20 with which base station reception beams can achievegood reception quality on the basis of the results of measurement of thereception quality of the sounding signals. Good reception qualityindicates a level in which the result of measurement of the receptionquality, such as the SINR, is equal to or higher than a presetthreshold. Note that, in order to select a terminal transmission beamwith which good reception quality can be achieved, the radio basestation 10 needs to distinguish a plurality of terminal transmissionbeams from the wireless terminal 20 from each other. Examples of methodsfor distinguishing a plurality of terminal transmission beams from thewireless terminal 20 at the radio base station 10 include a method ofassociating, by the wireless terminal 20, a sequence pattern on asounding signal to be transmitted by each terminal transmission beamwith a terminal transmission beam identifier (ID). The examples alsoinclude a method of associating, by the wireless terminal 20, the timeat which a sounding signal to be transmitted by each terminaltransmission beam with a terminal transmission beam ID. The examplesalso include a method of associating, by the wireless terminal 20, afrequency domain in which a sounding signal to be transmitted by eachterminal transmission beam is placed with a terminal transmission beamID. A terminal transmission beam ID is identification information foridentifying each terminal transmission beam, that is, informationcapable of identifying each of the terminal transmission beams 201 to206 in the example of FIG. 1. Note that, a method for generating asequence to be put on a sounding signal is described in 6.4.1.4.2 of3GPP specification TS 38.211 V15.0.0.

FIG. 2 is a diagram illustrating an example of frequency mapping of asounding signal transmitted by the wireless terminal 20 according to thefirst embodiment. Information on the frequency mapping illustrated inFIG. 2 shows association between frequency domains f1 to f6 in each ofwhich a sounding signal transmitted by the wireless terminal 20 isplaced and terminal transmission beam IDs. In FIG. 2, the terminaltransmission beam IDs are represented by 201 to 206. The wirelessterminal 20 transmits a sounding signal by each terminal transmissionbeam by using only the frequency domain assigned to the terminaltransmission beam. For example, the wireless terminal 20 transmits asounding signal by the terminal transmission beam 201 within thefrequency domain f1. The radio base station 10 is capable of determiningterminal transmission beams from the wireless terminal 20 with whichbase station reception beams can achieve good reception quality byspecifying information on frequency mapping illustrated in FIG. 2 to thewireless terminal 20 in advance.

FIG. 3 is a table illustrating an example of a result of selecting, foreach base station reception beam, a terminal transmission beam from thewireless terminal 20 achieving good reception quality at the radio basestation 10 according to the first embodiment. As illustrated in FIG. 3,at the radio base station 10, regarding the base station reception beam102, the sounding signal transmitted from the wireless terminal 20 bythe terminal transmission beam 202 has good reception quality. Inaddition, at the radio base station 10, regarding the base stationreception beam 103, the sounding signal transmitted from the wirelessterminal 20 by the terminal transmission beam 201 has good receptionquality. In addition, at the radio base station 10, regarding the basestation reception beam 106, the sounding signal transmitted from thewireless terminal 20 by the terminal transmission beam 205 has goodreception quality. In addition, at the radio base station 10, regardingthe base station reception beam 107, the sounding signal transmittedfrom the wireless terminal 20 by the terminal transmission beam 206 hasgood reception quality. FIG. 3 also illustrates that, at the radio basestation 10, good reception quality of the sounding signal transmittedfrom the wireless terminal 20 is not achieved regarding the base stationreception beams 101, 104, 105, and 108.

FIG. 3 further illustrates the association between each base stationreception beam at the radio base station 10 and a TRP group ID. A TRPgroup ID is information identifying each TRP group. In the exampleillustrated in FIG. 3, the TRP group ID of the TRP group associated withthe TRP #1 is represented by #1, and the TRP group ID of the TRP groupassociated with the TRP #2 is represented by #2. In the exampleillustrated in FIG. 3, the base station reception beams 101 to 104belong to TRP group ID #1, and the base station reception beams 105 to108 belong to TRP group ID #2.

The radio base station 10 notifies the wireless terminal 20 of theassociation between the terminal transmission beams from the wirelessterminal 20 achieving good reception quality and the TRP group IDs asillustrated in FIG. 3. For a method for the notification from the radiobase station 10 to the wireless terminal 20, layer 1 signaling using aphysical downlink control channel (PDCCH) defined in the NR standard,MAC signaling by a medium access control (MAC) layer, or the like isused. A specific example of the notification information contains: TRPgroup ID #1={terminal transmission beam 201, terminal transmission beam202}; and TRP group ID #2={terminal transmission beam 205, terminaltransmission beam 206}. This means that the radio base station 10grouped the terminal transmission beams 201 and 202 into the TRP groupID #1, and the terminal transmission beams 205 and 206 into the TRPgroup ID #2. The groups represented by the TRP group IDs #1 and #2 aregroups into which a plurality of terminal transmission beams from thewireless terminal 20 are grouped in units of TRPs #1 and #2, of theradio base station 10 at which signals transmitted by the terminaltransmission beams are received.

Next, a method by which the radio base station 10 controls thetransmission power of the wireless terminal 20 by using a transmissionpower control command will be explained. FIG. 4 is a diagramillustrating an example of a state in which the radio base station 10according to the first embodiment causes the wireless terminal 20 totransmit signals such as data by using the specified terminaltransmission beams 201, 202, 205, and 206. The radio base station 10specifies the terminal transmission beams of the wireless terminal 20 byusing UL grant defined in the NR standard. Format 0_1 of downlinkcontrol information (DCI) defined in 3GPP specification TS 38.212V15.0.0 is used for transmission of a message permitting the wirelessterminal 20 to perform PUSCH transmission, that is, the aforementionedUL grant. An “SRS resource indicator” is defined in a message of Format0_1, which specifies a beam of a sounding signal (sounding referencesignal: SRS) or a beam of a PUSCH signal using the same beam as thesounding signal. In addition, “TPC command for scheduled PUSCH” isdefined in the message of Format 0_1, which is a transmission powercontrol command. Note that, in the present embodiment, elements of thetransmission power control command are extended to correspond to thenumber of TRP groups. Specifically, when the number of TRP groups is n,the transmission power control command is defined as “TPC command forscheduled PUSCH #1”, “TPC command for scheduled PUSCH #2”, . . . , “TPCcommand for scheduled PUSCH #n”. In the present embodiment, the extendedformat will be referred to as Format 0_1E.

A case where the extended format of Format 0_1E is applied to theexample of FIG. 4 will be explained. FIG. 5 is a diagram illustrating anexample of a result of measurement of reception quality at each TRP ofthe radio base station 10 according to the first embodiment. Asdescribed above, assume that the reception quality indicates an SINR. Inthe example of FIG. 5, the SINR satisfies a proper SINR value at the TRP#1 while the SINR does not satisfy the proper SINR value at the TRP #2.In such a case, the radio base station 10 notifies the wireless terminal20 of a message containing content of the transmission power controlcommand. The content included in the message is: “TPC command forscheduled PUSCH #1=−1 [dB]”, “TPC command for scheduled PUSCH #2=+1[dB]”, and “SRS resource indicator={201,202,205,206}”.

Upon receiving the message including the aforementioned content, thewireless terminal 20 controls the transmission powers of the terminaltransmission beams in accordance with the content in the message. Asdescribed above, the wireless terminal 20 has separately received theinformation of TRP group ID #1={terminal transmission beam 201, terminaltransmission beam 202} and TRP group ID #2={terminal transmission beam205, terminal transmission beam 206}. The wireless terminal 20 uses theobtained information, and accumulates the transmission power by −1 [dB]from the value at the previous transmission for the TRP group ID #1 thatis, the group of the terminal transmission beams 201 and 202 andaccumulates the transmission power by +1 [dB] from the value at theprevious transmission for the TRP group ID #2, that is, the group of theterminal transmission beams 205 and 206.

Regarding the SINRs at the TRPs illustrated in FIG. 5, the radio basestation 10 is capable of lowering the SINR at the TRP #1 and increasingthe SINR at the TRP #2 by lowering the transmission power of theterminal transmission beams 201 and 202 of the wireless terminal 20 andincreasing the transmission power of the terminal transmission beams 205and 206 of the wireless terminal 20. In this manner, the radio basestation 10 is capable of making the SINR closer to the proper SINR valuein units of TRPs by controlling the transmission power of signalstransmitted by the wireless terminal 20 in units of TRPs, or morespecifically, the transmission power of the terminal transmission beams.

Next, a configuration of the radio base station 10 will be described.FIG. 6 is a diagram illustrating an example of a configuration of theradio base station 10 according to the first embodiment. The radio basestation 10 includes a signal processing unit 17, and antenna sections 14a and 14 b. The signal processing unit 17 includes a control unit 11, amodulation/demodulation unit 12, a transmission/reception unit 13, and ameasurement unit 15.

The control unit 11 instructs the wireless terminal 20 to transmit asounding signal, and associates the TRP group IDs, the base stationreception beams, and the terminal transmission beams with each other,that is, groups the TRP group IDs, the base station reception beams, andthe terminal transmission beams as illustrated in FIG. 3 on the basis ofthe reception quality of each sounding signal. In addition, the controlunit 11 selects a wireless terminal 20 to which a PUSCH is to beassigned, selects a terminal transmission beam of the wireless terminal20 with which good reception quality is achieved at each base stationreception beam, calculates a transmission power control value to beinstructed using a transmission power control command, controls thedirections of the base station reception beams, transmits and receivesdata to and from a core network, which is not illustrated, and the like.

The modulation/demodulation unit 12 modulates a signal, such as data andcontrol information, acquired from the control unit 11, and outputs themodulated signal to the transmission/reception unit 13. Themodulation/demodulation unit 12 also demodulates a signal acquired fromthe transmission/reception unit 13, and outputs the demodulated signalto the control unit 11.

The transmission/reception unit 13 converts a signal acquired from themodulation/demodulation unit 12 from a digital signal into an analogsignal, and up-converts the frequency thereof. Thetransmission/reception unit 13 outputs the analog signal obtained by theup-conversion to each of the antenna sections 14 a and 14 b. Thetransmission/reception unit 13 also down-converts the frequencies ofsignals acquired from the antenna sections 14 a and 14 b, and convertsthe signals from analog signals into digital signals. Thetransmission/reception unit 13 outputs the digital signals obtained bythe conversion to the modulation/demodulation unit 12.

The antenna sections 14 a and 14 b are base station antenna sectionsthat each generate a plurality of base station reception beams, andreceive, by using the base station reception beams, signals transmittedfrom the wireless terminal 20 using a plurality of terminal transmissionbeams.

Specifically, the antenna sections 14 a and 14 b each transmit signalsacquired from the transmission/reception unit 13 in corresponding beamdirections as instructed by the control unit 11. The antenna sections 14a and 14 b also receive signals from the wireless terminal 20 in beamdirections as instructed by the control unit 11. The antenna sections 14a and 14 b each generate a plurality of base station reception beams atthe same time. The measurement unit 15 measures the reception quality,the reception power, or the like of signals acquired from the antennasections 14 a and 14 b. Specifically, the measurement unit 15 measuresthe reception quality, the reception power, or the like of a signal foreach of the base station reception beams generated by the antennasections 14 a and 14 b. The measurement unit 15 outputs results ofmeasurements such as the reception quality, the reception power, or thelike to the control unit 11. The signals whose reception quality,reception power, or the like is measured by the measurement unit 15include the aforementioned sounding signal.

Operation of the radio base station 10 will be explained. FIG. 7 is aflowchart illustrating an operation of grouping the terminaltransmission beams of the wireless terminal 20, at the radio basestation 10 according to the first embodiment. For causing the wirelessterminal 20 to transmit a sounding signal and causing the measurementunit 15 to measure the reception quality of the sounding signal for eachof the base station reception beams 101 to 108 at the antenna sections14 a and 14 b, the control unit 11 generates frequency mapping asillustrated in FIG. 2. The control unit 11 generates control informationcontaining information on the frequency mapping and instructing totransmit a sounding signal, and transmits the control information to thewireless terminal 20 via the modulation/demodulation unit 12, thetransmission/reception unit 13, and the antenna section 14 a. In thismanner, the control unit 11 instructs the wireless terminal 20 totransmit a sounding signal (step S11). Upon receiving the controlinformation from the radio base station 10, the wireless terminal 20transmits a sounding signal in accordance with the control information.

For measurement of the reception quality of the sounding signal, thecontrol unit 11 indicates the directions of the base station receptionbeams to each of the antenna sections 14 a and 14 b and causes theantenna sections 14 a and 14 b to receive the sounding signal from thewireless terminal 20 (step S12). The measurement unit 15 receives thereceived signals from the antenna sections 14 a and 14 b, and measuresthe reception quality, that is specifically, the SINR for each of thereceived signals as described above (step S13). The measurement unit 15notifies the control unit 11 of the result of measurements of thereception quality. The control unit 11 groups the terminal transmissionbeams of the wireless terminal 20 on the basis of the result ofmeasurements from the measurement unit 15 (step S14). Specifically, thecontrol unit 11 generates a map indicating the relation of the TRP groupIDs, the base station reception beams, and terminal transmission beamsthat achieve good reception quality as illustrated in FIG. 3. Thecontrol unit 11 associates a TRP group ID with each terminaltransmission beam that achieves good reception quality from thegenerated map, and groups the terminal transmission beams of thewireless terminal 20 in units of TRPs of the radio base station 10.Specifically, the control unit 11 selects, for each base stationreception beam that has achieved preset reception quality, a terminaltransmission beam from the wireless terminal 20 used for transmission ofthe sounding signal received using the base station reception beam. Thecontrol unit 11 groups a plurality of terminal transmission beams of thewireless terminal 20 into groups in units of base station antennasections in such a manner that terminal transmission beams selected forbase station reception beams generated by one base station antennasection are grouped into the same group. The control unit 11 generatescontrol information containing group information on the grouping of theterminal transmission beams of the wireless terminal 20, and transmitsthe control information to the wireless terminal 20 via themodulation/demodulation unit 12, the transmission/reception unit 13, andthe antenna section 14 a. In this manner, the control unit 11 notifiesthe wireless terminal 20 of the group information of the terminaltransmission beams of the wireless terminal 20 (step S15). Note that,for transmitting the control information to the wireless terminal 20,that is, for notifying the wireless terminal 20 of the groupinformation, the radio base station 10 can transmit the controlinformation by using base station transmission beams generated by oneTRP that is monitored as a main TRP by the wireless terminal 20, forexample.

FIG. 8 is a flowchart illustrating an operation when a wireless terminal20 to which a PUSCH is to be assigned is selected in the radio basestation 10 according to the first embodiment. Upon selecting a wirelessterminal 20 to which a PUSCH is to be assigned (step S21), the controlunit 11 calculates a transmission power control value for each TRP group(step S22). The control unit 11 compares the SINRs of base stationreception beams at each TRP measured by the measurement unit 15 when thePUSCH has previously been received from the same wireless terminal 20with the proper SINR value, for example. The control unit 11 calculatesa transmission power control value for each TRP group on the basis ofthe result of comparison. The control unit 11 notifies the wirelessterminal 20 of the transmission power control value for the terminaltransmission beams of the wireless terminal 20 for each TRP group (stepS23). Specifically, the control unit 11 generates DCI Format 0_1E inwhich the transmission power control value for TRP group is a TPCcommand for scheduled PUSCH #1 to #2, and transmits the DCI Format 0_1Eto the wireless terminal 20 via the modulation/demodulation unit 12, thetransmission/reception unit 13, and the antenna section 14 a.

Next, a configuration of the wireless terminal 20 will be described.FIG. 9 is a diagram illustrating an example of a configuration of thewireless terminal 20 according to the first embodiment. The wirelessterminal 20 includes a control unit 21, a modulation/demodulation unit22, a transmission/reception unit 23, an antenna section 24, and asounding signal generating unit 25.

The control unit 21 analyzes the control information of which thewireless terminal 20 is notified from the radio base station 10, andinstructs transmission of a sounding signal, instructs transmission of aPUSCH, controls the transmission power for each group of terminaltransmission beams, controls the directions of the terminal transmissionbeams, and the like.

The modulation/demodulation unit 22 modulates a signal, such as data andcontrol information, acquired from the control unit 21, and outputs themodulated signal to the transmission/reception unit 23. Themodulation/demodulation unit 22 also demodulates a signal acquired fromthe transmission/reception unit 23, and outputs the demodulated signalto the control unit 21.

The transmission/reception unit 23 converts a signal acquired from themodulation/demodulation unit 22 from a digital signal into an analogsignal, and up-converts the frequency thereof. Thetransmission/reception unit 23 outputs the analog signal obtained by theup-conversion to the antenna section 24. The transmission/reception unit23 also down-converts the frequency of a signal acquired from theantenna section 24, and converts the signal from an analog signal into adigital signal. The transmission/reception unit 23 outputs the digitalsignal obtained by the conversion to the modulation/demodulation unit22.

The antenna section 24 is a terminal antenna section that generates aplurality of terminal transmission beams, and transmits signals to theradio base station 10 by using the plurality of terminal transmissionbeams. The antenna section 24 transmits a signal acquired from thetransmission/reception unit 23 in a beam direction as instructed by thecontrol unit 21. The antenna section 24 also receives a signal from theradio base station 10 in a beam direction as instructed by the controlunit 21. The antenna section 24 generates a plurality of terminaltransmission beams at the same time.

The sounding signal generating unit 25 is a measurement signalgenerating unit that generates a sounding signal on the basis of aninstruction from the control unit 21.

Operation of the wireless terminal 20 will be explained. FIG. 10 is aflowchart illustrating an operation until the wireless terminal 20according to the first embodiment acquires the group information of theterminal transmission beams of the wireless terminal 20 from the radiobase station 10. Upon acquiring control information instructing totransmit a sounding signal from the radio base station 10 via theantenna section 24, the transmission/reception unit 23, and themodulation/demodulation unit 22 (step S31), the control unit 21instructs the sounding signal generating unit 25 to generate a soundingsignal. In this process, the control unit 21 notifies the soundingsignal generating unit 25 of information of frequency mapping containedin the control information. The sounding signal generating unit 25generates a sounding signal for each terminal transmission beam on thebasis of the information of frequency mapping (step S32). In addition,the control unit 21 determines the directions of the terminaltransmission beams on the basis of the information of frequency mapping,and indicates the directions of the terminal transmission beams to theantenna section 24. The antenna section 24 generates terminaltransmission beams on the basis of the instruction from the control unit21, and transmits a sounding signal acquire from the sounding signalgenerating unit 25 via the transmission/reception unit 23, in each ofthe directions of the terminal transmission beam that are instructed bythe control unit 21 (step S33). As described above, the radio basestation 10 groups the terminal transmission beams of the wirelessterminal 20 on the basis of the reception quality of each of the basestation reception beams by which the sounding signal is received, andnotifies the wireless terminal 20 of a control signal including thegroup information. The control unit 21 acquires the control informationcontaining the group information from the radio base station 10 via theantenna section 24, the transmission/reception unit 23, and themodulation/demodulation unit 22. In this manner, the wireless terminal20 is capable of acquiring the group information generated by the radiobase station 10 (step S34).

FIG. 11 is a flowchart illustrating an operation of the wirelessterminal 20 according to the first embodiment when a PUSCH is assignedto the wireless terminal 20 by the radio base station 10. Upon acquiringDCI Format 0_1E from the radio base station 10 via the antenna section24, the transmission/reception unit 23, and the modulation/demodulationunit 22, the control unit 21 detects that a PUSCH is assigned to thewireless terminal 20 (step S41). The control unit 21 generates a signalto be transmitted to the radio base station 10, and outputs the signalto the modulation/demodulation unit 22. In addition, the control unit 21accumulates the transmission power control values for each group ofterminal transmission beams on the basis of “TPC command for scheduledPUSCH #1 to #2” and “SRS resource indicator” for each TRP groupcontained in the DCI Format 0_1E. Specifically, the control unit 21accumulates the transmission power control values for each group ofterminal transmission beams and determines the transmission power on thebasis of the information of TRP group ID #1={terminal transmission beam201, terminal transmission beam 202} and TRP group ID #2={terminaltransmission beam 205, terminal transmission beam 206}, which areacquired group information (step S42), and notifies the antenna section24 of the determined transmission power. The antenna section 24transmits signals to the radio base station 10 by using the terminaltransmission beams in accordance with the transmission power of whichthe antenna section 24 has been notified by the control unit 21 (stepS43).

Next, a hardware configuration for implementing the radio base station10 and the wireless terminal 20 will be described. FIG. 12 is a diagramillustrating an example of a hardware configuration for implementing theradio base station 10 and the wireless terminal 20 according to thefirst embodiment. The radio base station 10 is implemented by aprocessor 31, a memory 32, a transmitter 33, a receiver 34, and antennadevice 35, for example.

The processor 31 is a central processing unit (CPU; also referred to asa central processing device, a processing device, a computing device, amicroprocessor, a microcomputer, a processor or a digital signalprocessor (DSP)), a system large scale integration (LSI), or the like.The memory 32 is a nonvolatile or volatile semiconductor memory such asa random access memory (RAN), a read only memory (ROM), a flash memory,and an erasable programmable read only memory (EPROM), an electricallyerasable programmable read only memory (EEPROM: registered trademark), amagnetic disk, a flexible disk, an optical disk, a compact disc, a minidisc, a digital versatile disc (DVD), or the like.

The control unit 11 and the modulation/demodulation unit 12 of the basestation are implemented by the processor 31 and programs stored in thememory 32. Specifically, the control unit 11 and themodulation/demodulation unit 12 are implemented by the processor 31 byreading programs for performing operations of the units from the memory32 and executing the programs. The transmission/reception unit 13 isimplemented by the transmitter 33 and the receiver 34. Specifically,transmission processes of the transmission/reception unit 13 areperformed by the transmitter 33, and reception processes of thetransmission/reception unit 13 are performed by the receiver 34. Themeasurement unit 15 is also implemented by the receiver 34. The antennasections 14 a and 14 b are each implemented by the antenna device 35.

The wireless terminal 20 has a similar configuration. The control unit21, the modulation/demodulation unit 22, and the sounding signalgenerating unit 25 are implemented by the processor 31 and programsstore in the memory 32. Specifically, the control unit 11 and themodulation/demodulation unit 12 are implemented by the processor 31 byreading programs for performing operations of the units from the memory32 and executing the programs. The transmission/reception unit 23 isimplemented by the transmitter 33 and the receiver 34. Specifically,transmission processes of the transmission/reception unit 23 areperformed by the transmitter 33, and reception processes of thetransmission/reception unit 23 are performed by the receiver 34. Theantenna section 24 is implemented by the antenna device 35.

While Format 0_1E, which is an extension based on Format 0_1 defined inthe NR standard, is defined for transmission of the transmission powercontrol command for each TRP from the radio base station 10 to thewireless terminal 20 in the present embodiment, the format is notlimited to Format 0_1E. Any other format may be used as long as atransmission power control command corresponding to TPC command forscheduled PUSCH #1 to #n for each TRP group can be defined.

As described above, according to the present embodiment, in the casewhere the radio base station 10 includes a plurality of TRPs that areinstalled at different locations from each other, the radio base station10 performs transmission power control of the wireless terminal 20 onthe basis of the signal reception quality, such as the SINR, at eachTRP. Specifically, the radio base station 10 measures the receptionquality of a sounding signal transmitted from the wireless terminal 20for each base station reception beam at each TRP, groups a plurality ofterminal transmission beams directed toward one TRP, among a pluralityof terminal transmission beams generate by one wireless terminal 20,into one TRP group on the basis of the result of measurements, andperforms transmission power control in units of TRP groups. Thus, in thecase where signals from the wireless terminal 20 can be received at aplurality of TRPs, the radio base station 10 is capable of performingcontrol to make the SINR at each of the TRPs close to the proper SINRvalue by controlling the transmission power of the signals transmittedby the wireless terminal 20 in units of TRPs at which the signals are tobe received. In addition, because the radio base station 10 does notperform transmission power control in units of terminal transmissionbeams, transmission power control can be performed without unnecessarilyincreasing the number of transmission power control commands, whichreduces the increase in the overhead of control during communication.

Second Embodiment

In the first embodiment, the radio base station 10 groups the terminaltransmission beams of the wireless terminal 20. In a second embodiment,a case where the wireless terminal groups the terminal transmissionbeams will be described. In the second embodiment, assume that so-calledbeam correspondence, which means that base station transmission beamsand base station reception beams form the same gain patterns as eachother, is satisfied at each of the TRPs of the radio base station. Thebase station transmission beams are transmission beams generated at therespective TRPs of the radio base station of the second embodiment fortransmission of signals to the wireless terminal.

In addition, assume that the so-called beam correspondence, which meansthat terminal transmission beams and terminal reception beams form thesame gain patterns as each other, is satisfied in the wireless terminalas well. The terminal reception beams are reception beams generated inthe wireless terminal of the second embodiment for reception of signalsfrom the radio base station.

FIG. 13 is a diagram illustrating an example of a configuration of aradio communication system 50 a according to the second embodiment. Theradio communication system 50 a includes a radio base station 10 a, anda wireless terminal 20 a. The radio base station 10 a includes a signalprocessing unit 17 a, and antenna sections 14 a and 14 b. The radio basestation 10 a performs radio communication with the wireless terminal 20a by using the antenna sections 14 a and 14 b. The antenna sections 14 aand 14 b generate base station reception beams 101 to 104 and basestation reception beams 105 to 108, respectively, and receive signalstransmitted from the wireless terminal 20 a by using the base stationreception beams 101 to 104 and the base station reception beams 105 to108, respectively, in a manner similar to the first embodimentillustrated in FIG. 1. In addition, in the present embodiment, theantenna sections 14 a and 14 b generate base station transmission beams111 to 114 and base station transmission beams 115 to 118, respectively,and transmit signals to the wireless terminal 20 a by using the basestation transmission beams 111 to 114 and the base station transmissionbeams 115 to 118, respectively, as illustrated in FIG. 13. The wirelessterminal 20 a generates six terminal transmission beams 201 to 206, andtransmits signals to the radio base station 10 a by using the terminaltransmission beams 201 to 206, in a manner similar to the wirelessterminal 20 illustrated in FIG. 1. In addition, in the presentembodiment, the wireless terminal 20 a generates terminal receptionbeams 211 to 216, and receives signals transmitted from the radio basestation 10 a by using the terminal reception beams 211 to 216 asillustrated in FIG. 13. While the number of wireless terminals 20 a inthe radio communication system 50 a is one in FIG. 13, the number ofwireless terminals 20 a may be two or more.

Specifically, in the present embodiment, assume that base stationreception beams 101 to 108 correspond to base station transmission beams111 to 118, respectively, the base station reception beams 101 to 108and the base station transmission beams 111 to 118 form the same gainpatterns as each other, and thus beam correspondence is satisfied in theradio base station 10 a. In addition, assume that terminal transmissionbeams 201 to 206 correspond to terminal reception beams 211 to 216,respectively, the terminal transmission beams 201 to 206 and theterminal reception beams 211 to 216 form the same gain patterns as eachother, and thus beam correspondence is satisfied in the wirelessterminal 20 a.

When beam correspondence is satisfied, the radio base station 10 anotifies the wireless terminal 20 a of information as illustrated inFIG. 14. FIG. 14 is a table illustrating an example of information onthe relation of TRP group IDs and base station transmission beams whichis notified by the radio base station 10 a to the wireless terminal 20 ain the second embodiment. In this manner, the radio base station 10 anotifies the wireless terminal 20 a of the information on base stationtransmission beams to be used for transmission at each TRP. The radiobase station 10 a may notify all the wireless terminals 20 a in commonof the information illustrated in FIG. 14 as notification information,or may individually notify the wireless terminals 20 a of theinformation.

A wireless terminal 20 a that has acquired the information on theassociation between the TRP group IDs and the base station transmissionbeams, associates a base station transmission beam with a terminalreception beam. As illustrated in FIG. 13, the wireless terminal 20 ameasures the reception quality of each of the terminal reception beams211 to 216 to select which of the terminal reception beams 211 to 216 touse to receive signals transmitted using the base station transmissionbeams 111 to 118 from the radio base station 10 a. FIG. 15 is a tableillustrating the association between the base station transmission beams111 to 118 selected from the result of measurements of the receptionquality for each of the terminal reception beams 211 to 216 and theterminal reception beams 211 to 216 of the wireless terminal 20 aaccording to the second embodiment.

As illustrated in FIG. 15, the wireless terminal 20 a achieves the bestreception quality when receiving, by using the terminal reception beam213, a signal transmitted from the radio base station 10 a using thebase station transmission beam 111. In addition, the wireless terminal20 a achieves the best reception quality when receiving, by using theterminal reception beam 212, a signal transmitted from the radio basestation 10 a using the base station transmission beam 112. In addition,the wireless terminal 20 a achieves the best reception quality whenreceiving, by using the terminal reception beam 211, a signaltransmitted from the radio base station 10 a using the base stationtransmission beam 113. In addition, the wireless terminal 20 a achievesthe best reception quality when receiving, by using the terminalreception beam 214, a signal transmitted from the radio base station 10a using the base station transmission beam 115. In addition, thewireless terminal 20 a achieves the best reception quality whenreceiving, by using the terminal reception beam 215, a signaltransmitted from the radio base station 10 a using the base stationtransmission beam 116. In addition, the wireless terminal 20 a achievesthe best reception quality when receiving, by using the terminalreception beam 216, a signal transmitted from the radio base station 10a using the base station transmission beam 117. FIG. 15 also illustratesthat, at the wireless terminal 20 a, there are no terminal receptionbeams that achieved good reception quality concerning signalstransmitted from the radio base station 10 a using the base stationtransmission beams 114 and 118.

A signal transmitted from the radio base station 10 a and used formeasurement of the reception quality at the wireless terminal 20 a, is asynchronization signal (SS) or a channel state information-referencesignal (CSI-RS) defined in the NR standard. Either of the signals is asignal that is periodically transmitted from the radio base station 10a. An SS is added with an index that identifies each base stationtransmission beam. A CSI-RS uses a different time-frequency resource fordifferent base station transmission beam. Thus, in both cases ofreceiving either of an SS and a CSI-RS, the wireless terminal 20 a iscapable of distinguishing which base station transmission beam was usedfor transmission of the signal.

The wireless terminal 20 a that has associated the base stationtransmission beams with the terminal reception beams is capable ofassociating a TRP group ID with a terminal transmission beam by usingthe information illustrated in FIGS. 14 and 15 because beamcorrespondence is satisfied in both of the radio base station 10 a andthe wireless terminal 20 a. In this manner, the wireless terminal 20 ais capable of generating groups of terminal transmission beams in unitsof TRPs of the radio base station 10 a. Specifically, the wirelessterminal 20 a is capable of determining that terminal transmission beams201, 202, and 203 associated with the terminal reception beams 211, 212,and 213 are grouped into the same group of TRP group #1, and thatterminal transmission beams 204, 205, and 206 associated with terminalreception beams 214, 215, and 216 are grouped into the same group of TRPgroup #2. Note that the operations of the radio base station 10 a andthe wireless terminal 20 a other than the grouping are similar to thoseof the radio base station 10 and the wireless terminal 20, respectively,in the first embodiment.

Next, a configuration of the radio base station 10 a will be described.FIG. 16 is a diagram illustrating an example of a configuration of theradio base station 10 a according to the second embodiment. The radiobase station 10 a includes a signal processing unit 17 a, and antennasections 14 a and 14 b. The signal processing unit 17 a corresponds tothe signal processing unit 17 of the first embodiment illustrated inFIG. 6 but additionally includes a measurement signal generating unit16. The measurement signal generating unit 16 generates a measurementsignal, that is specifically, an SS or a CSI-RS as described above, inaccordance with an instruction from the control unit 11. In the radiobase station 10 a, the control unit 11 further causes the measurementsignal generating unit 16 to generate an SS or a CSI-RS to enablegrouping of a plurality of terminal transmission beams at the wirelessterminal 20 a in units of base station antenna sections by which thesignals are to be received in the radio base station 10 a, in additionto the operation explained in the first embodiment. The control unit 11indicates the directions of the base station transmission beams to theantenna sections 14 a and 14 b for transmission of the SS or the CSI-RS.The control unit 11 also generates control information containing theinformation on the association between the TRP group IDs and the basestation transmission beams illustrated in FIG. 14, and notifies thewireless terminal 20 a of the control information via themodulation/demodulation unit 12, the transmission/reception unit 13, andthe antenna section 14 a.

Operation of the radio base station 10 a will be explained. FIG. 17 is aflowchart illustrating an operation of transmitting a measurement signaland control information to the wireless terminal 20 a that groupsterminal reception beams, in the radio base station 10 a according tothe second embodiment. The control unit 11 causes the measurement signalgenerating unit 16 to generate a measurement signal, that isspecifically, an SS or a CSI-RS as described above. The measurementsignal generating unit 16 generates a measurement signal (step S51). Themeasurement signal generating unit 16 outputs the measurement signal toeach of the antenna sections 14 a and 14 b via thetransmission/reception unit 13. The control unit 11 also determines thedirections of base station transmission beams, and indicates thedirections of the base station transmission beams to the antennasections 14 a and 14 b. The antenna sections 14 a and 14 b generate aplurality of base station transmission beams on the basis of theinstruction from the control unit 11, and transmit the measurementsignal, which is acquired from the measurement signal generating unit 16via the transmission/reception unit 13, by using each of the basestation transmission beams in the directions of the base stationtransmission beams as indicated by the control unit 11 (step S52). Thecontrol unit 11 also generates control information containing theinformation on the association between the TRP group IDs and the basestation transmission beams (step S53). The control unit 11 notifies thewireless terminal 20 a of the control information via themodulation/demodulation unit 12, the transmission/reception unit 13, andthe antenna section 14 a (step S54). Note that the operations of theradio base station 10 a when a wireless terminal 20 a to which a PUSCHis to be assigned is selected, are similar to those of the radio basestation 10 in the first embodiment illustrated in FIG. 8.

Next, a configuration of the wireless terminal 20 a will be described.FIG. 18 is a diagram illustrating an example of a configuration of thewireless terminal 20 a according to the second embodiment. The wirelessterminal 20 a corresponds to the wireless terminal 20 of the firstembodiment illustrated in FIG. 9 but additionally includes a measurementunit 26. The measurement unit 26 measures the reception quality, thereception power, or the like of a measurement signal received using eachterminal reception beam acquired from the antenna section 24 to generatethe association between the base station transmission beams and theterminal reception beams as illustrated in FIG. 15. Specifically, themeasurement unit 26 measures, for each of the terminal reception beams,the reception quality, the reception power, or the like when measurementsignals transmitted from the radio base station 10 a are received byusing the terminal reception beams generated by the antenna section 24.The measurement unit 26 notifies the control unit 21 of the result ofmeasurements. Upon receiving the result of measurements, the controlunit 21 generates the map illustrated in FIG. 15. The control unit 21acquires control information on the association between the TRP groupIDs and the base station transmission beams as illustrated in FIG. 14separately from the radio base station 10 a, and finally determines theassociation between the TRP group IDs and the terminal transmissionbeams.

Operation of the wireless terminal 20 a will be explained. FIG. 19 is aflowchart illustrating an operating of grouping terminal transmissionbeams of the wireless terminal 20 a at the wireless terminal 20 aaccording to the second embodiment. For measurement of the receptionquality of measurement signals transmitted from the radio base station10 a, the control unit 21 instructs the directions of the terminalreception beams to the antenna section 24 and causes the antenna section24 to receive the measurement signals from the radio base station 10 a(step S61). The measurement unit 26 receives the received signals fromthe antenna section 24, and measures the reception quality, that isspecifically, the SINR as described above (step S62). The measurementunit 26 reports the reception quality, that is, the result ofmeasurements of the SINR to the control unit 21. In addition, theantenna section 24 receives control information containing theinformation on the association between the TRP group IDs and the basestation transmission beams from the radio base station 10 a (step S63).The antenna section 24 outputs the received control information to thecontrol unit 21 via the transmission/reception unit 23 and themodulation/demodulation unit 22. The control unit 21 groups the terminaltransmission beams of the wireless terminal 20 a on the basis of theacquired result of measurements and the control information (step S64).In this manner, the control unit 21 selects, for each terminal receptionbeam, a base station transmission beam of the radio base station 10 aused for transmission of the measurement signal received by the terminalreception beam on the basis of the reception quality. The control unit21 groups the terminal transmission beams associated with the terminalreception beams in units of base station antenna sections of the radiobase station on the basis of the terminal reception beams, for whichbase station transmission beams generated by the same base stationantenna section of the radio base station 10 a are selected. Note thatthe operations of the wireless terminal 20 a when a PUSCH is assigned tothe wireless terminal 20 a by the radio base station 10 a, are similarto those of the wireless terminal 20 in the first embodiment illustratedin FIG. 11.

Regarding the hardware configuration of the radio base station 10 a, themeasurement signal generating unit 16 included in addition to the radiobase station 10 of the first embodiment is implemented by the processor31 illustrated in FIG. 12 and programs stored in the memory 32illustrated in FIG. 12. In addition, regarding the hardwareconfiguration of the wireless terminal 20 a, the measurement unit 26included in addition to the wireless terminal 20 of the first embodimentis implemented by the receiver 34 illustrated in FIG. 12.

As described above, according to the present embodiment, in the casewhere beam correspondence is satisfied in both of the radio base station10 a and the wireless terminal 20 a, the wireless terminal 20 a groupsthe terminal transmission beams. In this case as well, the same effectsas those in the first embodiment are produced.

Third Embodiment

While the radio base station 10 transmits transmission power controlcommands correspondingly associated with TRP groups at the same time tothe wireless terminal 20 in the first embodiment, the transmission powercontrol commands need not necessarily be transmitted at the same time.In a third embodiment, a case where the radio base station 10 transmitstransmission power control commands one by one, each command beingassociated with one TRP group at timings different from each other willbe explained. Although this case is also applicable to the radio basestation 10 a of the second embodiment, an example of application to theradio base station 10 of the first embodiment will be explained becausethe operations in the second embodiment are similar to those in thefirst embodiment.

In the third embodiment, only one definition of a transmission powercontrol command “TPC command for scheduled PUSCH” is sufficient, and theradio base station 10 alternatively notifies the wireless terminal 20 ofthe TRP group ID, to which the TPC command for scheduled PUSCH is to beapplied. Specifically, information on a TRP group ID is added to anyregion defined in a message of the aforementioned Format 0_1. The formatto which the information of the TRP group ID is added will be referredto as Format 0_1EE, for example. The radio base station 10 generates amessage containing “TRP group ID=#1” and “TPC command for scheduledPUSCH=−1 [dB]” by using the Format 0_1EE, and notifies the wirelessterminal 20 of the message at a first timing, for example. In addition,the radio base station 10 generates a message containing “TRP groupID=#2” and “TPC command for scheduled PUSCH=+1 [dB]” by using the Format0_1EE, and notifies the wireless terminal 20 of the message at a secondtiming, for example. Specifically, in the radio base station 10, thecontrol unit 11 performs an operation of notifying the wireless terminal20 of a transmission power control value in units of TRP groups atdifferent transmission timings for different TRP groups. Note that theoperations such as determination on the association between the TRPgroup IDs and the terminal transmission beams in the radio base station10 are similar to those in the first embodiment.

Upon acquiring “TRP group ID” and “transmission power control command”through the message of the Format 0_1EE, the wireless terminal 20accumulates the transmission power control command values for each groupof terminal transmission beams. Although the difference from the firstembodiment lies in that the wireless terminal 20 acquires a message foreach TRP group ID, the operation of accumulating the transmission powercontrol command values after acquisition of the message of the Format0_1EE is similar to that in the first embodiment.

Note that the radio base station 10 can perform transmission powercontrol only on TRP groups the SINR, which is reception quality, ofwhich has not reached the proper SINR value, instead of controllingtransmission power for all the TRP groups. In a case where TRP #1 andTRP #2 are present and the SINR of TRP #1 has not reached the properSINR value while that of TRP #2 has reached the proper SINR value, forexample, the radio base station 10 notifies the wireless terminal 20 ofa transmission power control command for TRP #1 only. Specifically, inthe radio base station 10, the control unit 11 performs an operation ofnotifying the wireless terminal 20 of a transmission power control valuefor the TRP group for which the transmission power needs to be changed.

In addition, in a case where control for increasing the transmissionpower is needed for all of a plurality of TRP groups but it isdetermined that the increase in the transmission power for all the TRPgroups will result in an excess of the transmission power of thewireless terminal 20 over maximum transmission power, the radio basestation 10 can select one or more TRP groups that are more important,and increase the transmission power for the selected TRP group(s). Inthis case, the radio base station 10 notifies the wireless terminal 20of a transmission power control command for the selected TRP group only.The method for selecting a more important TRP group in the radio basestation 10 may be selecting a TRP associated with a base stationreception beam with the lowest SINR, for example. Note that a mechanismfor the wireless terminal 20 to periodically notify the radio basestation 10 of a difference between the maximum transmission power andthe current transmission power is already defined in the NR standard.Thus, the radio base station 10 is capable of easily determining whetherthe transmission power of the wireless terminal 20 exceeds the maximumtransmission power. The radio base station 10 may change the number ofTRP groups to be selected on the basis of the difference between themaximum transmission power and the current transmission power of thewireless terminal 20. Specifically, in the radio base station 10, in acase where the transmission power of the wireless terminal 20 exceedsthe maximum transmission power if the transmission power is increasedfor a plurality of TRP groups, the control unit 11 performs an operationof notifying the wireless terminal 20 of a transmission power controlvalue for some TRP group(s) selected from a plurality of TRP groups.

As described above, according to the present embodiment, the radio basestation 10 notifies the wireless terminal 20 of a plurality oftransmission power control commands one by one, the commands beingassociated with a plurality of TRP groups, at a timing different fromeach other. Thus, in a case where the number of TRP groups is large, theradio base station 10 is capable of reducing the increase in the numberof control bits necessary for one transmission of a transmission powercontrol command.

In addition, the radio base station 10 notifies the wireless terminal 20of a transmission power control command only for one or more TRP groupsthe SINR of each of which has not reached the proper SINR value. Thisenables the radio base station 10 to reduce the overhead of control forTRP groups on which the control need not be performed.

In addition, in a case where the transmission power of the wirelessterminal 20 exceeds the maximum transmission power if the transmissionpower is increased for a plurality of TRP groups, the radio base station10 selects one or more important TRP groups, and performs control ofincreasing the transmission power for the selected TRP group(s) only.Thus, the radio base station 10 is capable of preventing thetransmission power of the wireless terminal 20 from exceeding themaximum transmission power and making the SINR for a TRP on whichcontrol is needed closer to the proper value.

Fourth Embodiment

In the first to third embodiments, the radio base station controls thetransmission power of the wireless terminal always in units of TRPgroups. In a fourth embodiment, a case where the radio base station 10performs transmission power control in units of TRP groups ortransmission power control in common for all the TRP groups depending onconditions, will be explained. Although this case is also applicable tothe radio base station 10 a of the second embodiment and to the radiobase station 10 and the radio base station 10 a of the third embodiment,an example of application to the radio base station 10 of the firstembodiment will be explained because the operations in the second andthird embodiments are similar to those in the first embodiment.

For example, in the wireless terminal 20, when a data unit that is asection in transmitting or retransmitting a signal is a codeword, thereare a method of mapping one codeword to all the terminal transmissionbeams used for transmission and a method of mapping in units of terminaltransmission beams or beam groups. FIG. 20 is a diagram illustrating anexample of a mapping pattern in which the wireless terminal 20 accordingto the fourth embodiment maps one codeword in all the terminaltransmission beams to be used for transmission. In addition, FIG. 21 isa diagram illustrating an example of a mapping pattern in which thewireless terminal 20 according to the fourth embodiment maps onecodeword in units of terminal transmission beams. The patternillustrated in FIG. 20 will be referred to as a mapping pattern A, andthe pattern illustrated in FIG. 21 will be referred to as a mappingpattern B. The wireless terminal 20 maps one codeword into a pluralityof layers in accordance with a mapping pattern defined in the NRstandard. Furthermore, for mapping from each of the layers to beams, thewireless terminal 20 uses a technology called precoding. In the NRstandard, beams are called antenna ports. Beams illustrated in FIGS. 20and 21 correspond to the terminal transmission beams in the first tothird embodiments. The wireless terminal 20 performs a matrix operationon a signal of each layer, and maps the operation result to the beams.Note that examples of a matrix used for the matrix operation ofprecoding are described in Chapter 6.3.1.5 of 3GPP specification TS38.211 V15.0.0.

Note that, the mapping pattern A is selected or the mapping pattern B isselected depending on the matrix used in the wireless terminal 20.First, assume a case where the mapping pattern A illustrated in FIG. 20is selected in the wireless terminal 20, a signal is transmitted bybeams a and b toward the TRP #1, and a signal is transmitted by beams eand f toward the TRP #2. Even when a condition as illustrated in FIG. 5,for example, occurs at the TRPs #1 and #2 in the radio base station 10that receives the signal, there is no problem just as long as the SINRat the TRP #1 and the TRP #2 have reached the proper SINR value ifinterference with other radio base stations need not be considered. Insuch a case, it is sufficient that the radio base station 10 controlsthe wireless terminal 20 with one transmission power control command asin the related art. For example, such a case where no other radio basestation using the same frequency is present around the radio basestation 10 can be assumed. In contrast, in a case where interferencewith another radio base station needs to be considered, when thecondition as illustrated in FIG. 5 occurs at the TRPs #1 and #2, theradio base station 10 preferably performs transmission power control onthe wireless terminal 20 in units of TRP groups. In such a case, theradio base station 10 selects the mapping pattern B as the pattern to beused by the wireless terminal 20, and performs transmission powercontrol in units of TRP groups if the wireless terminal 20 hastransmitted a signal toward the TRP #1 by using beam group 1 and asignal toward the TRP #2 by using beam group 2.

The radio base station 10 determines whether to use the mapping patternA or the mapping pattern B, that is, whether to perform transmissionpower control in units of groups or in common for all the groups on thebasis of whether interference with another radio base station ispresent. The NR standard states that the radio base station 10 notifiesthe wireless terminal 20 of the result of determination on which of themapping patterns A and B is selected by using “precoding information” inthe Format 0_1. In this manner, when the transmission power control ofthe wireless terminal 20 is to be performed for each TRP group in viewof the condition of communication with the wireless terminal 20, theradio base station 10 uses the Format 0_1E described in the firstembodiment or the Format 0_1EE described in the second embodiment. Whenthe transmission power control of the wireless terminal 20 is to beperformed in common for all the TRP groups, the radio base station 10uses the existing Format 0_1. In this manner, the radio base station 10is capable of using two modes. In addition, a method in which the radiobase station 10 determines either one mode to be always used, andnotifies the wireless terminal 20, with which the radio base station 10is to communicate, of the mode only once when starting the communicationcan be considered.

FIG. 22 is a flowchart illustrating an operation of determining atransmission power controlling method for the wireless terminal 20 inthe radio base station 10 according to the fourth embodiment. In a casewhere transmission power control of the wireless terminal 20 is needed,when interference with another radio base station needs to be considered(step S71: Yes), the control unit 11 determines that transmission powercontrol in units of TRP groups is effective, and determines to controlthe transmission power of the terminal transmission beams of thewireless terminal 20 in units of TRP groups (step S72). Wheninterference with another radio base station need not be considered(step S71: No), the control unit 11 determines that the transmissionpower control in units of TRP groups is not necessary, and determines tocontrol the transmission power of the terminal transmission beams of thewireless terminal 20 in common for the TRP groups (step S73).

As described above, according to the present embodiment, the radio basestation 10 performs transmission power control in common for the TRPgroups when interference with another radio base station need not beconsidered, and performs transmission power control in units of TRPgroups when interference with another radio base station needs to beconsidered. This enables the radio base station 10 to appropriatelycontrol the reception quality such as the SINR for each TRP group byperforming the transmission power control in units of TRP groups wherenecessary, and to reduce the overhead of control of the entire systemwhen the transmission power control in common for the TRP groups issufficient.

While the terminal transmission beams are grouped in units of TRPs inthe first to third embodiments, the grouping method is not limited tothat in units of TRPs. For example, when signals transmitted by theterminal transmission beams are received, the radio base station maygroup the terminal transmission beams of the wireless terminal in viewof similarity in reception quality or difference in reception quality.

The configurations presented in the embodiments above are examples ofthe present invention, and can be combined with other known technologiesor can be partly omitted or modified without departing from the scope ofthe present invention.

A radio base station according to the present invention produces aneffect of controlling transmission powers of signals transmitted by awireless terminal in units of locations at which the signals arereceived in a case where signals from a wireless terminal can bereceived at a plurality of locations.

What is claimed is:
 1. A wireless terminal that performs radiocommunication with a radio base station including a plurality of basestation antenna devices, the wireless terminal comprising: a terminalantenna device to generate terminal transmission beams, and transmitsignals to the radio base station by using the terminal transmissionbeams; a processor, and a memory to store a program which, when executedby the processor, performs operations of: generating measurement signalswhich are the signals for measurement of reception quality at the radiobase station, receiving control information from the base station, thecontrol information indicating association between at least some of theterminal transmission beams and the base station antenna devices of theradio base station based on the measurement signals, determiningtransmission power of the terminal transmission beams on the basis of aninstruction from the radio base station in units of groups correspondingto the control information.
 2. The wireless terminal according to claim1, wherein the processor generates the measurement signal on the basisof an instruction from the radio base station, and the terminal antennadevice generates terminal transmission beams on the basis of theinstruction from the processor, and transmits the measurement signal tothe radio base station.
 3. A control circuit to control a wirelessterminal that performs radio communication with a radio base stationincluding a plurality of base station antenna devices, to performoperations of: generating measurement signals for measurement ofreception quality at the radio base station, causing a terminal antennadevice to generate terminal transmission beams, and transmit themeasurement signals to the radio base station by using the terminaltransmission beams; and receiving control information from the basestation, the control information indicating association between at leastsome of the terminal transmission beams and the base station antennadevices of the radio base station based on the measurement signals,determining transmission power of the terminal transmission beams on thebasis of an instruction from the radio base station in units of groupscorresponding to the control information.
 4. A non-transitory programstorage medium storing a program for causing a wireless terminal, whichperforms radio communication with a radio base station including aplurality of base station antenna devices, to perform: generatingmeasurement signals for measurement of reception quality at the radiobase station, controlling a terminal antenna device to generate terminaltransmission beams, and transmit the measurement signals to the radiobase station by using the terminal transmission beams; and receivingcontrol information from the base station, the control informationindicating association between at least some of the terminaltransmission beams and the base station antenna devices of the radiobase station based on the measurement signals, determining transmissionpower of the terminal transmission beams on the basis of an instructionfrom the radio base station in units of groups corresponding to thecontrol information.